Purified chick embryo brain actin will be separated into its individual micro-heterogeneous forms by preparative isoelectric focusing in 8 M urea. The isolated components will be compared via amino acid analysis and peptide mapping with the average analyses obtained on samples of purified brain and muscle actins. Actin from peripheral nerve tissue, neuroblastoma cells and glioma cells will be compared to the purified brain actin by electrophoretic and peptide mapping techniques in order to determine the similarities between the microheterogeneous forms in these specific cell types. The effects of ions (Ca ions, Mg ions, K ions, Na ions) on actin assembly will be evaluated in purified brain and muscle actin monomer samples. Conformational changes which take place in actin upon assembly will be followed by circular dichroism spectra of monomer and trimer samples of actin isolated by gel filtration. Comparisons between brain actin and muscle actin assembly by difference circular dichroism measurements will also be made. In addition, other brain proteins which interact with actin will be isolated by affinity chromatography on a column containing F-actin. The effects of these proteins on the assembly and morphology of actin filaments will be evaluated by electron microscopy. Factors affecting the cold stability of microtubules in the CNS of hibernating mammals will be examined. The assembly characteristics of tubulin isolated from hibernating squirrel brain will be compared to those of rat brain tubulin to determine if modifications in either the tubulin dimer or the microtubule associated proteins have occurred.